In some aspects, the invention relates to an antibody-drug conjugate, comprising an antibody； a linker； and at least two active agents. In preferred embodiments, the linker comprises a peptide sequence of a plurality of amino acids, and at least two of the active agents are covalently coupled to side chains of the amino acids. The antibody-drug conjugate may comprise a self-immolative group, preferably two-self-immolative groups. The linker may comprise an O-substituted oxime, e.g., wherein the oxygen atom of the oxime is substituted with a group that covalently links the oxime to the active agent； and the carbon atom of the oxime is substituted with a group that covalently links the oxime to the antibody.
